ABSTRACT
Parietal neuronal populations have been found which respond bimodally to visual and somatosensory input regarding one's own limbs or even perceived haptic input of a false limb (Graziano et al., Science 290:1782-1785, 2000). Further, neuronal populations have been observed which respond preferentially to visual stimuli presented in spatial congruence with our hands (Graziano, Proc Natl Acad Sci USA 96:10418-10421, 1999). In this study, we examined event-related potentials (ERPs) elicited by laser dots projected onto or above participants' index and middle fingers during a sustained-attention task. We hypothesized that visual stimuli projected onto the hand would elicit differences in ERP deflections related to sensory gating and categorization in comparison to when projected close to the hand. Participants responded via a footswitch to rare target flashes of light occurring on or directly above the middle finger of the attended hand. We found enhanced amplitudes of the N1 and P3 deflections when the stimuli fell onto the finger tips as opposed to above them. Furthermore, the N1 for unattended stimuli was less suppressed when the lasers were projected onto the fingers. Behaviorally, participants were less accurate to targets when the lasers fell onto the fingers. We conclude that when the lasers appear to "touch" the participants, they act to automatically draw participants' attention. Thus visual stimuli projected onto the fingers of the 'unattended' hand are harder to filter out, leading to decreases in accuracy during task performance.
Subject(s)
Cerebral Cortex/physiology , Evoked Potentials/physiology , Illusions/physiology , Touch Perception/physiology , Visual Perception/physiology , Adult , Attention/physiology , Brain Mapping , Cerebral Cortex/anatomy & histology , Electroencephalography , Female , Fingers/innervation , Fingers/physiology , Humans , Lasers , Light , Male , Mechanoreceptors/physiology , Neurons, Afferent/physiology , Neuropsychological Tests , Photic Stimulation , Psychomotor Performance/physiology , Young AdultABSTRACT
Further processing of auditory stimuli in the free field is attenuated when participants are in contact with speakers versus not touching them. Studies in the visual domain have found that men and women use different strategies for processing spatial information. In this study, we examined sex-related differences in event-related potentials while men and women performed an auditory discrimination task in peripersonal space when either holding speakers or resting their hands in their laps. We found that men responded more accurately than women to targets in attended locations, and that the sexes exhibited different event-related potential patterns during task performance. These differences are consistent with existing predictions of female top-down and male bottom-up strategies in spatial processing.
